Role of Non-Structural Sugar Metabolism in Regulating Tuber Dormancy in White Yam (Dioscorea rotundata)

Abstract

Changes in sugar composition occur continuously in plant tissues at different developmental stages. Tuber dormancy induction, stability, and breaking are very critical developmental transitions in yam crop production. Prolonged tuber dormancy after physiological maturity has constituted a great challenge in yam genetic improvement and productivity. In the present study, biochemical profiling of non-structural sugar in yam tubers during dormancy was performed to determine the role of non-structural sugar in yam tuber dormancy regulation. Two genotypes of the white yam species, one local genotype (Obiaoturugo) and one improved genotype (TDr1100873), were used for this study. Tubers were sampled at 42, 56, 87, 101, 115, and 143 days after physiological maturity (DAPM). Obiaoturugo exhibited a short dormant phenotype and sprouted at 101-DAPM, whereas TDr1100873 exhibited a long dormant phenotype and sprouted at 143-DAPM. Significant metabolic changes were observed in non-structural sugar parameters, dry matter, and moisture content in Obiaoturugo from 56-DAPM, whereas in TDr1100873, significant metabolic changes were observed from 101-DAPM. It was observed that the onset of these metabolic changes occurred at a point when the tubers of both genotypes exhibited a dry matter content of 60%, indicating that a dry matter content of 60% might be a critical threshold for white yam tuber sprouting. Non-reducing sugars increased by 9–10-fold during sprouting in both genotypes, which indicates their key role in tuber dormancy regulation in white yam. This result implicates that some key sugar metabolites can be targeted for dormancy manipulation of the yam crop.

Comparative Metabolomics Profiling Reveals Key Metabolites and Associated Pathways Regulating Tuber Dormancy in White Yam (<em>Dioscorea rotundata</em>)

“…our result is an agreement with the findings of [94,95] and the report of Wengler; [92]. Also, we earlier reported that biochemical profiling of non-structural sugar from yam tuber dormancy to dormancy break revealed that quantity of nonreducing sugar which include sucrose increased up to 9 and 10 folds in the tubers of TDr110073 and Obiaoturugo respectively and that this increase started from 56-DAPM in tubers of Obiaoturugo and 101-DAPM in tubers of TDr1100873 [44]. This Indicates that sucrose play role in the early cellular activities culminating in dormancy break in the tubers of both genotypes.…”

“…while botanical seeds are in desiccation state at maturity necessitating their requirement of imbibition during germination process, yam tubers at maturity are in hydrated state, and do not require imbibition during germination. Instead, as we reported earlier [44], it requires moisture loss to 40% threshold before dormancy breaking process can commence.…”

“…It has been reported that aromatic amines, and amino acids reduced the thickness and increased seed tegument porosity which helped in water imbibition and boost seed germination rate [91]. whereas in yam tuber, the reverse is the case, as we earlier reported that yam tuber required moisture reduction to critical threshold of 40% before dormancy breaking process could be initiated [44]. Study has also demonstrated that phenolics, aromatic amines and amino acids in exerting their antioxidant property inhibit enzymes that generate ROS in a cell system [68], in doing this, they might also inhibit enzymes that catalyze the removal of cell cycle arrest at G1 phase, thereby preventing the resumption of mitotic cell division which mark endodormancy break.…”

“…It is believed that yam tuber dormancy induction is an adaptive response to low energy condition due to stoppage of supply of sugar from photosynthesis as result of vine senescence at tuber physiological maturity [44]. Since photosynthetic sugar supply and mineral uptake systems are not active during yam tuber dormancy, the energy needs for low and high physiological activities during tuber dormancy is supplied from reserved energy-source metabolites in the tuber [45].…”

Comparative Metabolomics Profiling Reveals Key Metabolites and Associated Pathways Regulating Tuber Dormancy in White Yam (Dioscorea rotundata Poir.)

“…While botanical seeds are in the desiccation state at maturity, necessitating their requirement of imbibition during the germination process, yam tubers at maturity are in the hydrated state, and do not require imbibition during germination. Instead, as we reported earlier [ 44 ], it requires moisture loss to a 40% threshold before the dormancy-breaking process can commence. This might be linked to this sharp deviation of yam tuber germination stages from well-established three curve stages of the germination process in botanical seeds.…”